1. Field of the Invention
The present invention relates to an ink jet head for applying pressure to pressure chambers and thus ejecting ink drops from nozzles, and in particular to a multi-nozzle ink jet head for performing lead out of electrodes from a row of piezoelectric bodies using a laminate of the elements.
2. Description of the Related Art
An ink jet recording head has nozzles, ink chambers, an ink supply system, an ink tank, and transducers; by transmitting displacement/pressure generated by the transducers to the ink chambers, ink particles are ejected from the nozzles, and characters or images are recorded on a recording medium such as paper.
In a well-known form, a thin-plate-shaped piezoelectric element having the whole of one surface thereof bonded to the outer wall of an ink chamber is used as each transducer. A pulse-like voltage is applied to the piezoelectric element, thus bending the composite plate comprising the piezoelectric element and the outer wall of the ink chamber, and the displacement/pressure generated through the bending is transmitted to the inside of the ink chamber via the outer wall of the ink chamber.
A sectioned perspective view of a conventional multi-nozzle ink jet head 100 is shown in FIG. 21. As shown in FIG. 21, the head 100 is constituted from a row of piezoelectric bodies 111, individual electrodes 112 that are formed on the piezoelectric bodies, a nozzle plate 114 in which are provided nozzles 113, ink chamber walls 117 made of a metal or a resin that, along with the nozzle plate 114, form ink chambers 115 corresponding to the nozzles 113, and a diaphragm 116.
A nozzle 113 and a piezoelectric body 111 are provided for each ink chamber 115, and the periphery of each ink chamber 115 and the periphery of the corresponding part of the diaphragm 116 are connected together strongly. A piezoelectric body 111 for which a voltage has been applied to the individual electrode 112 deforms the corresponding part of the diaphragm 116 as shown by the dashed lines in the drawing. As a result, an ink drop is ejected from the nozzle 113.
Application of voltages to each of the piezoelectric bodies 111 is carried out separately using electrical signals from a printing apparatus main body via printed circuit boards. FIG. 22 is a drawing showing the constitution of connections between the conventional head and the printed circuit boards. In the example of FIG. 22, the head 100 has 8 rows and 8 columns of nozzles 113, i.e. of piezoelectric bodies 111 and individual electrodes 112. Corresponding to this, flexible printed circuit boards 110 are provided for connecting the driver circuitry of the apparatus and the individual electrodes 112 together.
In this prior art, the terminals of the printed circuit boards 110 are connected to the respective individual electrodes 112 by wires 120 through wire bonding. Moreover, art in which an FPC wiring board is connected directly is also known.
Moving on, due to demands to increase printing resolution, there are demands to increase the density of the nozzle arrangement of heads. If the nozzle density is raised, then the contact spacing between terminals (individual electrodes) is reduced. For example, the nozzle density of a head using piezoelectric bodies is currently about 150 dpi, but is advancing to 180xcx9c300 dpi, and further to 360 dpi, and hence the contact spacing is becoming lower. However, currently the best contact spacing with wire bonding using semiconductor manufacturing is 150 dpi, with 300 dpi contacts being developed in the case of FPC connection.
Consequently, if electrical connection is carried out by providing contacts on top of or near to the piezoelectric bodies 111 as conventionally, then a problem of joining of neighboring contacts (shorting) may arise. Moreover, when connecting a large number of points in a short time, the load on the piezoelectric bodies 111 becomes very high, and with thin-film piezoelectric bodies there is a risk of breakage, and hence connection is extremely problematic.
It is an object of the present invention to provide a multi-nozzle ink jet head for carrying out connection at a position away from the driving parts of the pressure chambers, thus preventing there being an effect on the driving characteristics even if a load is applied during the connection.
Moreover, it is another object of the present invention to provide a multi-nozzle ink jet head for preventing a lag in the driving operation of the piezoelectric bodies relative to the input waveform even though the led out wiring parts have a piezoelectric body actuator laminated structure.
Furthermore, it is yet another object of the present invention to provide a multi-nozzle ink jet head for preventing expansion and contraction of the piezoelectric bodies at the led out wiring parts even though these wiring parts have a piezoelectric body actuator laminated structure.
To attain these objects, one form of the multi-nozzle ink jet head of the present invention has a head substrate in which are formed a plurality of nozzles and a plurality of pressure chambers, a diaphragm that also acts as a common electrode and covers the plurality of pressure chambers, piezoelectric body layers that are provided in correspondence with the pressure chambers on the diaphragm, individual electrode layers that are provided on the piezoelectric body layers and have individual electrode parts corresponding to the pressure chambers and wiring parts for the individual electrode parts, and a low-dielectric layer or an insulating layer that is provided between the piezoelectric body layers and the diaphragm in the region of the wiring parts.
Firstly, a novel multi-nozzle ink jet head structure for which a PCT application (PCT/JP/99/06960) was filed by the present applicant on Dec. 10, 1999 is a prerequisite of the present invention. With this structure, the piezoelectric body layers are provided even in regions other than the regions of the pressure chambers, and wiring parts from the individual electrodes are formed on the piezoelectric body layers, and hence connection to the outside of the head can be carried out at a position away from the row of the piezoelectric bodies of the pressure chambers.
The present invention further improves the characteristics of a head of this structure, improving the drop in the characteristics caused by the wiring parts having the piezoelectric body actuator laminated structure. That is, with the structure described above, the electrical capacitance of the wiring parts is added, and hence a lag arose in the driving operation of the piezoelectric bodies relative to the input waveform, and moreover the piezoelectric bodies expanded and contracted at the wiring parts, and hence there was a risk of structural problems (structural cross talk, breaking off of joining parts etc.) arising in the head.
With the present form of the present invention, by forming a low-dielectric layer or an insulating layer between the piezoelectric body layers and the diaphragm in the region of the wiring parts, the electrical capacitance of the wiring parts can be reduced. A lag in the driving operation due to the electrical capacitance can thus be prevented, and moreover structural problems in the head can be prevented.
Moreover, with the multi-nozzle ink jet head of the present invention, by constituting the low-dielectric layer or insulating layer from a flattening layer that flattens between the piezoelectric body layers. The layer for reducing the above-mentioned electrical capacitance can be formed during the flattening layer formation step, and hence the manufacturing process can be shortened.
The multi-nozzle ink jet head of another form of the present invention has a head substrate in which are formed a plurality of nozzles and a plurality of pressure chambers, a diaphragm that also acts as a common electrode and covers the plurality of pressure chambers, piezoelectric body layers that are provided in correspondence with the pressure chambers on the diaphragm, and individual electrode layers that are provided on the piezoelectric body layers and have individual electrode parts corresponding to the pressure chambers and wiring parts for the individual electrode parts, wherein the diaphragm is provided in a region other than the region of the wiring parts.
With this form of the present invention, the diaphragm is not formed at the wiring parts, and hence the electrical capacitance of the wiring parts can be eliminated. Moreover, expansion and contraction of the piezoelectric bodies at the wiring parts can be prevented.
Moreover, with the multi-nozzle ink jet head of the present invention, by providing an insulating layer in the region of the wiring parts in the same layer position as the diaphragm, breakage of the wiring parts can be prevented.
A multi-nozzle ink jet head of yet another form of the present invention has a head substrate in which are formed a plurality of nozzles and a plurality of pressure chambers, a diaphragm that also acts as a common electrode and covers the plurality of pressure chambers, piezoelectric body layers that are provided in correspondence with the pressure chambers on the diaphragm, and individual electrode layers that are provided on the piezoelectric body layers and have individual electrode parts corresponding to the pressure chambers and wiring parts for the individual electrode parts, wherein the diaphragm has a common electrode layer provided in a region other than the region of the wiring parts, and a rigid layer.
With this form of the present invention, in a head having a structure with a laminated type diaphragm (electrode layer, plus rigid layer having mechanical strength), the electrode layer of the diaphragm is not formed at the wiring parts, and hence the constitution is such that the electrical capacitance of the wiring parts is eliminated, and moreover expansion and contraction at the wiring parts is eliminated.
With the multi-nozzle ink jet head of the present invention, by providing the rigid layer in the regions of both the wiring parts and the individual electrode parts, breakage of the wiring parts can be prevented.
Other objects and forms of the present invention will become apparent from the following description of embodiments and the drawings.